Electric switch



Dec."30, 1947.1 F. P.'GAssER ELECTRIC SWITCH Filed Oct. 7, 1942 .Q f55.1. o

HL2-95m i l 52 ATToQ/vfy Patented Dec. 30, 1947 ELECTRIC SWITCH Frank P.Gasser, Beverly Farms, Mass., assignor to Harry M. Burt and Guy II.Burt, doing business as The Lloyd Products Company, Providence, R. I.

Application October 7, 1942, Serial No. 461,098

4 Claims.

This invention relates to electric switches of the type which provide alow impedance path when a high potential is applied thereto,automatically change the low impedance path to a high impedance pathafter a short time lag, and effectively maintain such high impedancepath if the applied potential is lowered.

More particularly, the invention is concerned with an improved startingswitch adapted to be used with an electric discharge lamp of the typehaving at least one thermionic electrode which must be heated to anelectron emissive temperature before discharge can be initiated in thelamp. The switch connects the lamp electrodes in series.

At the present time, starters for such electric discharge lamps are oftwo types; the rst having a pair of normally spaced contacts, and thesecond a pair of normally closed contacts.

Switches of the rst class have at least one contact mounted on a thermalresponsive element and are provided with electrically energizablethermal emissive means connected in parallel with the contacts. Thethermal emissive means is of such nature that when potential is appliedto an unlit lamp, the heat generated by said means will raise thetemperature of the thermal responsive element and cause the contacts tomove into engagement. Since the switch connects the lamp electrodes inseries, closing of the contacts provides a low impedance path betweensaid electrodes and passes a high current through the same, causing thethermionic electrode to be heated to the desired temperature. Engagementof the contacts also bypasses the current which energizes the thermalemissive means, allowing the thermal responsive element to cool off, sothat shortly after closing of the contacts they will reopen. If the lampstarts upon reopening of the contacts, its low running impedance soreduces the potential applied to the thermal emissive means thatinsufilcient heat is generated thereby to again close the contacts. If,however, the lamp does not start, its high idle impedance reduces thecurrent flow and allows a high enough potentialv to again be applied tothe thermal emissive means to create sufficient heat to close thecontact for a Second time. This second closing and subsequent reopeningof the contacts (upon shunting of the thermal emissive means) is knownas recycling, and is essential because on occasion, the lamp will failto start upon the rst starting try, i. e., when the contacts are rstreopened. This failure to start may be due to a variety of causes, suchfor example, as opening of the contacts at a moment when the potential(Cl. 20G-122) of switches is that, since the switches employ normallyspaced contacts, arcing occurs both when the contacts approach andrecede from each other before and after engagement. The two arcingscause the starting switch to have a very short life. Also due to thenormally spaced position of the contacts and resultant multiple arcings,contact resistance increases rapidly and raises the resistance of thelow impedance path through the switch thus lowering the temperature towhich the thermionic electrodes are raised. Another detrimental featureof these switches is that recycling is performed on the same contacts asthose used fcr'making the rst starting try.

Switches of the second class have-at least one of their contacts mountedon a thermally responsive element and are provided with electricallyenergizable thermal emissive means in series with the contacts anddisposed in the main supply circuit for the discharge lamp. Whenpotential is rst applied, the closed contacts provide a low impedancepath between the thermionic electrodes and allow a heating current-l tolilow therethrough. This same current flows through the thermal emissivemeans and, after a predetermined time, generates sufcient heat toactuate the thermal responsive element and separate the contacts. If thelamp does not light when the contacts are separated, the thermalresponsive element cools off, since 'the opening ofthe contacts breaksthe series circuit, and recycling occurs. On the other hand, if the lampdoes start, suilcient current passes through the thermal emissive meansto keep the contacts open. Switches of this latter class, like switchesof the first class, recycle on the same pair of contacts as thoseemployed to make the first starting eiort and are thus subject toconsiderable wear which appreciably shortens their lives. These switchesavoid the initial movement of the contacts towards each other and arcingarising from such movement. However, they only avoid this defect byemploying four terminals, two for the contacts and two for the thermalresponsive element in contrast with the two terminals employed inswitches of the rst class. Thus, the gain in longevity of the switch ismade at the expense of a more complicated starting circuit andadditional switch parts.

It is the primary object of the present invention to provide an improvedswitch of the character described which incorporates al1 the desirablefeatures ofthe Vabove described types of switches, but avoids theVinherent defects thereof.

More particularly it is an object' of my invention to provide a switchof the character described in which different pairs of contacts are usedfor the rst starting try and for recycling` A more specic object of myinvention is to provide a switch of the character .described-in which asingle contact cooperates' with a pair of electrically connectedcontacts, with one of which it causes an initial starting attempt to bemade, and with the other of which it. causes subsequent startingattempts to be made,

An ancillary object of my invention is to provide a switch of thecharacter described in which the vcontact resistanceA iskept.; low,arcing between contacts lessened, andthe escape of fumes upon'separation of the contacts; minimized.` Y

Another object of my inventionistogprovide a switch ofthe characterdescribed which employs only two terminals, includesy relatively few andsimple parts, is easily fabricated, durable, and in generalhighlyeflicientin use'.

Otherobjects of this invention will in part be obviousand inpartghereinafter pointed out.

The invention accordinglylconsists in' the featuresfof construction,combinations of' elements, and arrangement of Darts which will beexemplilied` in the construction hereinafter described.'

andof which the scope of application will be indicated in the claims. 1

In the accompanying drawings,v in which is shown one of. the variouspossible embodiments of thisY invention,

Fig.. 1.'i`s a schematic circuit diagram for a fluorescent electricdischarge lamp, the starter switch embodying my invention beingillustrated inA perspective; l

Fig. 2 isa side elevational View ofsaid` switch showing the contacts intheir initial starting position; and

Figs. 3' and 4 are similar fragmentary views thereof showing thecontacts in running and recycling vpositions respectively.

Referring now to the` drawings, and more particu-.larly to Figs. 1-4, Ihave there shown a fluorescent electric discharge tube I of the standardtype comprising. an elongate-dy pellucid vitreousy envelope I2 which isinternally coated withv suitable phosphore. The 'tube ends are sealedlofi and the tube iilledwith a gaseousv ionizable medium at a properpressure. Two spaced lamentary electrodes I4 are enclosed within thetube. `These electrodesY may be fashioned from or coated with materialwhich when raised to an elevated temperature at or approachingincandes'cence will emit electrons.

A. suitable supply of electric energy, such as an alternating' currentsource,v is. connected' to an end' of each' electrode l4 throughIlead-inwires t6, Il', one of which has "the usual manually operat'ed'switch 20,and the usual ballast coil 22 series-connected therein. The other endsof the electrodesare connected by leads 24, 26- to a l starting switch28 constructed in accordance with my invention.

Said starting switchcomprises a base disc 30 oi insulating material fromwhich electrically conductive terminals 32, 34 project, the same beingadapted to be detachably received in a customary starting socket (notshown). A tubular shell 36 cooperates with the base 30 to enclose theoperative elements of the switch.

A conductor wire 38 connected to the terminal 32 projects upwardly fromthe base 36. A similarly' disposed conductor Wire 46 is connected to theterminal 34. Said two wires have angularly disposed portions 42, 44received in aperatures in a partition 46 of insulating material wherebyto support said partition vertically within the shell 36. Extensions 48,50 of the conductor wires 38, 46 onthe other side of the partition 46lead to a condenser 52.

An elongated bimetallic strip 54 is disposed on v the side of thepartition opposite the condenser 52` and is held in substantiallyvertical position by means of a supporting wire 56 welded to the lowerend ofthe strip and secured to said partition. The upper end of thebimetallic strip 54 is free and has welded thereto a cylindricalmetallic contact 58 which projects laterally from said strip'. The strip54 is so fashioned that when heated it will move the contact 58 awayfrom the partition 461 Potential is applied to the bimetallicstrip 54from the terminal 32 and conductor wire. 38 through a low impedanceresistor 60 which may take the formV of a short helix of small diameterandlarge pitch. Said helix is disposed immediately adjacent saidbimetallic strip near its point of cantilever support on the wire 56.

A second bimetallic strip 62 is connected to the conductor wire 40 bymeans of a lead wire 64 which retraverses the partition 46 to provide arm support for said second strip. Saidr second strip is disposedhorizontally and transversely of the rst bimetallic strip 54, and is sofashioned that when heat is applied thereto, the free end of the secondstrip 52 will move away from the partition 46. As is well known, thisconstruction enables the switch to operate uniformly regardless of theroom temperature.

The free ends of the two bimetallic strips are disposed in closeproximity. The free end of the horizontal strip 62 has welded thereon aU-shaped metallic member 66 including a base 68 which interconnects twovertically disposed, spaced contact legs 10, 'l2 which lie substantiallyin a. vertical plane perpendicular to the partition 46. Said metalliccontact legs 70, I2 are so disposed as to lie in the path of travel ofthe contact member 58 when the latter` is actuated by movement of Ithebimetallic strip 54 upon the variation in temperature of the latterrelative to the temperature of the second strip 62. Furthermore, the twobimetallic strips and the various contact elements4 58, lI0, I2 are soconstructed and arrangedl that when the strips are at the sametemperature the contact element 58 will be pressed by the rst strip 54against the contact element 16 as shown in Fig. 2.

A high impedance resistor 'I4 is connected by wires 16, 18 across theterminals 32, 34, and is thus electrically disposed in parallel with thecontacts 58, 10, T2. Said resistor is physically disposed above the lowimpedance resistor 60 and adjacent the rst strip 54.

In the operation of a fluorescent tube I2 employing a switch 28embodying my invention, the hand operated switch 20 is first closed.This allows current to flow through the ballast reactor 22, one of thelamentary electrodes I4, the low impedance path through the switch 28,and the other nlamentary electrode I4. Said low impedance path betweenthe terminals 32, 34 includes, in series connection, the conductor wire38, low impedance resistor B0, bimetallic strip 54, contact element 58,contact element 10, base 68, contact element 12, strip 62, lead wire 64,and conductor wire 40. The resistance offered by this low impedance pathis so small that a high current will pass through the lamentaryelectrodes I4, thereby raising said electrodes to an electron emissivetemperature. While the temperature of the electrodes is being thuselevated the heavy current traversing the low impedance resistor 80generates heat which is applied to the bimetallic strip 54 near itscantilever mounting. Said strip 54 and resistor 68 are so relativelyproportioned and arranged that after a short period of a few seconds,during which the filamentary electrodes I4 will have had suflicient timeto be raised to electron emissive temperature, the strip 54 will moveits contact element 58 away from the contact leg 10. When this occursthe surge potential induced by the ballast reactor 22 will be appliedacross the electrodes I4 in an attempt to strike a dischargetherebetween.

If the discharge occurs, the impedance of the tube I0 is suddenlyreduced from the high impedance offered by the non-ionized gaseousmedium to the low impedance of the ionized space between said electrodeswhen the tube is lit. The large illuminating current now flowing willraise the potential drop in the electrodes I4 and reactor 22 and cause alower potential to be applied to the switch 28. This lowered potential,however, will flow enough current through the shunting, high impedanceresistor 14 to generate sufficient heat to keep the bimetallic strip 54warped enough to maintain the contact element 58 disposed spaced awayfrom the contact leg 18. This amount of heat is not sulicient to warpthe bimetallic strip 54 to such a degree that the contact element 58will engage the contact leg 12. This intermediate or floating positionof the Contact element 58 is illustrated in Fig. 3 and represents thedisposition of the various operative parts during running operation ofthe tube I0.

It will be appreciated that during the foregoing first try of thestarter switch, the Contact elements 58, only move apart so that an arcis struck but once. It will further be understood that little or no heatis generated in the vicinity of these contacts so that at the time thatthe arc is struck the contacts are at relatively low temperature andwill not be greatly degenerated to increase contact resistance andliberate objectionable fumes. Also, by employing a construction whichoperates in the foregoing manner, the low resistance path through theswitch 28 which makes the iirst try can be held to a very smallimpedance thereby allowing a maximum heating current to flow through theiilamentary electrodes I4.

If discharge in the tube I0 is not initiated upon separation of thecontacts 58 and 18, the impedance oifered by the tube I0 remains highand voltage drop through the reactor 22 small, so that a greaterpotential will be applied to the switch 28 than when the tube is lit.This potential is applied to the high impedance resistance 14, andbecause a larger current is passing through this resistance than whenthe tube is lit, the heat generated thereby will warp the bimetallicstrip 54 to a greater extent than indicated in the floating positionshown in Fig. 3. The warping at such time is suflicient to press thecontact 58 into engagement with the contact leg 12, as

shown in Fig. 4. This is the recycling position of the switch. In thisposition a low impedance path is again formed between the terminals 32,34. This path includes conductor wire 38, low impedance resistor 60,bimetallic strip 54, Contact 58, contact leg 12, bimetallic strip 62,and conductor wires 64 and 40. Said low resistance path enables a highheating current to pass through the filamentary electrodes I4 and againheats said electrodes to incandescence. However, the abutting of thecontacts 58, 12 forms a low impedance shunt path across the highimpedance resistor 14, causing said resistor and the strip 54 to cooland allowing the contact 58 to retract from the contact leg 12. It maybe mentioned that the current passing through the low impedance resistor60 when the contacts 58, 12 are closed does not generate suflicient heatto maintain the strip 54 in the recycling position shown in Fig. 4. Inaddition abutment of the strip 54 against the resistor 14 in the oatingposition inhibits further warping of said strip under the innuence ofsaid low impedance resistor. When the contacts 58, 12 separate, a surgepotential will once again be applied between electrodes I4 in a secondattempt to strike a discharge therebetween.

If the discharge fails to occur upon first disengagement of the contacts58, 12 from recycling position, an increased potential will be reappliedto the resistor 14, once more distorting the strip 54 and urging thecontact 58 against the contact leg 12. The recycling will continuebetween the contacts 58, 12 until the lamp is lit or until the switch 28is rendered inoperative.

If the lamp lights after disengagement of the recycling contacts 58, 12,insunicient potential is applied to the resistor 14 to distort the strip54 suiiiciently to reengage the contacts 58, 1'2, However, enoughpotential is applied to keep the strip' 54 in such distorted positionthat the contact 58 lies or floats between the two contact legs 10, 12as shown in Fig. 3.

The impedance values of the low and high resistors 68 and 14 are sochosen as to effect the above described operation. For purposes ofillustration, and without in any way limiting my invention to any ofthese values, it may be mentioned that on a 110 volt supply circuit andwith a li0-watt fluorescent discharge lamp, a resistance of 15,000 ohmsfor the high impedance 74 and 3.7 ohms for the low impedance willfunction satisfactorily. It will, of course, be understood that thesevalues may be varied within wide r ranges depending upon the type ofbimetallic strips, the spacing of the various contacts, and the spacingand disposition of the resistors relative to the bimetallic strips andcontacts.

Various possible embodiments may be made of the above invention andvarious changes may be made in the embodiment set forth withoutdeparting from the spirit of the invention. It will therefore beunderstood that al1 matter herein set forth or shown in the accompanyingdrawings is to be interpreted as illustrative and not in a limitingsense.

It will thus be seen that there is provided a device in which theseveral objects of this invention are achieved, and which is welladapted to meet the conditions of practical use.

Having thus described my invention, I claim as new and desire to secureby Letters Patent:

l, An electric switch adapted to be used for starting an electricdischarge lamp having at least one thermionic electrode, said switchcomprising a pair of electrically connected spaced con-- tact members, athird contact member normally in contact with one of said pair ofmembers, at least one bimetallic strip for effecting relative movementJof said third member and said pair of members, said bimetallic strip andsaid contact members bei -g so constructed that upon heating of saidstrip said third contact member and the other of said pair of contactmembers are caused to approach each other, a low impedance resistorelectrically connected in series with said contact members and arrangedin heat transfer relationship with said bimetallic strip, and a highimpedance resistor electrically connected in parallel with said contactmembers and also arranged in heat transfer relationship with saidbimetallic strip, said high impedance resistor being so constructed andpositioned that the heat generated thereby when said contacts are openand said lamp is lit will sunice only to maintain said contacts open andthat the heat generated thereby when potential is applied to said lampwith the lamp unlit and the contact members open will cause said thirdmember to contact the other of said pair` of members, said bimetallicstrip being supported at an end thereof remote from said contact membersand said low impedance resistor being disposed closer to said point ofsupport than said high impedance resistor, said bimetallic stripabutting said high impedance resistor when the heat generated by saidlow impedance resistor causes said third contact member and the first ofsaid pair of contact members to be separated.

2. An electric two-terminal switch adapted to be used for starting anelectric discharge lamp having at least one thermionic electrode, saidswitch comprising a pair f electrically connected spaced contact memberspermanently electrically connected to a switch terminal, a third contactmember normally in contact with one of said pair oi members andpermanently electrically connecte-d to the other terminal of the switch,at least one bimetallic strip for effecting relative movement of saidthird member and said pair of members, said bimetallic strip and saidcontact members being so constructed that upon heating oi said stripsaid third contact member will leave said one of the pair of contactmembers and approach the other of the pair of contact members, a lowimpedance resistor permanently electrically connected in series in acornmon circuit for all of said contacts and arranged in heat transferrelationship with said bimetallic strip, and a high impedance resistorpermanently electrically connected in parallel with said contact membersand also arranged in heat trans-- fer relationship with the samebimetallic strip, said high impedance resistor being so constructed andpositioned that the heat generated thereby, when said contacts are openand said lamp is lit, will sunice only to maintain said contacts openand that the heat generated thereby, when potential is applied to saidlamp with lamp unlit and the contact members open, will warp said stripto such an extent as to cause said third member to contact the other ofsaid pair of members, said bimetallic strip being supported at an endthereof remote from the Contact members and the low impedance resistorbeing disposed closer to said point of support than the high impedanceresistor, said bimetallic strip abutting said high impedance resistorwhen the heat generated by said low impedance resistor causes the thirdcontact member and the first of the pair oi contact members to beseparated.

3. An electric two-terminal switch adapted to be used for starting anelectric discharge lamp having at least one thermionic electrode, saidswitch comprising a pair of electrically connected spaced contactmembers permanently electrically connected to a switch terminal, a thirdcontact member normally in contact with one of said pair of members andpermanently electrically connected to the other terminal of the switch,at least one bimetallic strip for effecting relative movement or saidthird member and said pair of members, said bimetallic strip and saidcontact members being so constructed that upon heating or" said stripsaid third contact member will leave said one of the pair of contactmembers and approach the other of the pair of contact members, a lowimpedance resistor permanently electrically connected in series in acommon circuit for all of said contacts and arranged in heat transferrelationship with said bimetallic strip, and a high impedance resistorpermanently electrically connected in parallel with said Contact membersand also arranged in heat transfer rclationship with the same bimetallicstrip, said high impedance resistor being so constructed andpositionedthat the heat generated thereby, when said contacts are open and saidlamp is lit, will suilce only to maintain said contacts open and thatthe heat generated thereby, when potential is applied to said lamp withlamp unlit and the contact members open, will warp said strip to such anextent as to cause said third member to contact the other of said pairof members, said bimetallic strip being supported at an end thereofremote from the contact members and the low impedance resistor beingdisposed closer to said point of support than the high impedanceresistor, said bimetallic strip abutting said high impedance resistorwhen the heat generated by said low impedance resistor causes the thirdcontact member and the iirst of the pair of contact members to beseparated, and the heat generated by said low impedance resistor beinginsufcient to warp said bimetallic strip to such an extent as tomaintain said third contact member and the other of said pair of contactmembers in contact.

4. An electric two-terminal switch adapted to be used for starting anelectric discharge lamp having at least one thermionic electrode, saidswitch comprising a pair of electrically connected spaced contactmembers permanently electrically connected t0 a switch terminal, a thirdcontact member normally in contact with one of said pair of members andpermanently electrically connected to the other terminal of the switch,at least one bimetallic strip for effecting relative movement or" saidthird member and said pair of members, said bimetallic strip and saidcontact members being so constructed that upon heating of said stripsaid third contact member will leave said one of the pair of Contactmembers and approach the other of the pair of contact members, a lowimpedance resistor permanently electrically connected in series in acommon circuit for all of said contacts and arranged in heat transferrelationship with said bimetallic strip, and a high impedance resistorpermanently electrically connected in parallel with said contact membersand also arranged in heat transfer relationship with the same bimetallicstrip, said high impedance resistor being so constructed and positionedthat the heat generated thereby, when said contacts are open and saidlamp is lit,

REFERENCES CITED The following references are of record in the le ofthis patent:

Number UNITED STATES PATENTS Name Date McCarthy Apr. 4, 1944 McCarthyAug. 10, 1943 Bensin Oct. 19, 1943 Abbott Dec. 30, 1941 McCarthy June 9,1942 Lord Aug. 25, 1942 Gustin et al. Oct. 6, 1942 Hall Dec. 15, 1942

